The Gelechiidae are a family of moths commonly referred to as twirler moths or gelechiid moths. They are the namesake family of the huge and little-studied superfamilyGelechioidea, and the Gelechiidae's relationships with and delimitation against their relatives have been subject to considerable dispute. These are generally very small moths with narrow, fringed wings. The larvae of most species feed internally on various parts of their host plants, sometimes causing galls. Douglas-fir (Pseudotsuga) is a host plant common to many species of the family, particularly of the genusChionodes which is consequently more diverse in North America than usual for Gelechioidea.[1]

By the late 20th century, over 900[2] genera with altogether more than 4,500 species were placed here, with about 650 known from North America alone. While these figures are certainly outdated due to the many of reevaluations of Gelechioidea and new descriptions of twirler moths, they still serve to give an impression of the enormous biodiversity contained in this important family.

The voracious habits of their larvae make twirler moths suitable for biological control of invasive plants. The spotted knapweed seedhead moth (Metzneria paucipunctella), for example, is used to control spotted knapweed (Centaurea maculosa) in North America. Even more subtle plant-host interactions have been discovered in these moths. The Guatemalan potato moth may become a harmful pest. If it is not entirely eradicated from a potato field, but allowed to infest some plants (up to around 20% in one study[3]), the overall harvest will increase, and include an increased number of extremely large tubers.

Compared to the other massively diverse Gelechioidea families – Coleophoridae (case-bearers) and Oecophoridae (concealer moths) – the systematics of the Gelechiidae are far less contentious. The "Deoclonidae", sometimes treated as a full gelechioid family, seem to be nothing other than a specialized offshoot from within the Gelechiidae, and are here included in the present family; some authors differ, however, and ally at least some of these genera with the Autostichinae and/or Symmocidae. On the other hand, the Schistonoeidae (scavenger moths) are preliminarily considered a distinct family here.[4][5][6][7][8]

Of the subfamilies traditionally accepted for the Gelechiidae, only three are maintained here pending further information; at least one other, the Physoptilinae, may also be valid. But numerous genera of twirler moths – including most of the former "Deoclonidae" and for the time being also the proposed Physoptilinae – are of undetermined affiliation at present. The subfamilies, along with some notable genera, are:[6][7]